Various applications, such as article inspection and measurements, as well as lithography processing, require precise movement of the article with respect to a processing tool along a vertical axis (Z-axis). For example, in the manufacture of semiconductor devices, as well as testing of circuits on semiconductor wafers, the wafer is typically supported on a stage mounted for a Z-axis movement (Z-stage) and sometimes also for rotation (Z/Theta stage).
U.S. Pat. No. 5,150,040 discloses a dual mode Z/Theta stage for supporting and moving a workpiece, such as a semiconductor wafer, for positioning during testing. The Z/Theta stage has a peripheral four-point elevator drive. The elevating suspension comprises parallel, vertically oriented, rigid lift pins, which bear the weight of a top-plate. The lift pins are located about the periphery of the stage to provide stability of the support. The top plate essentially floats on the lift pins so that virtually no frictional forces are translated to lift pins. The lift pins are elevated together by the force of four matched pin lift levers, crank arms. The crank arms are driven by downward force from a vertically translating air piston, which is in contact with the crank arms. The air piston provides a gentle force moderated by pneumatic pressure, which can moderate the full force of a stepping motor that drives it.